CAPE TOWN, May 4 (Reuters) - A South African court will hear a claim on May 18 involving a seized Moroccan ship that the Polisario movement in Western Sahara complained was carrying phosphate taken illegally from the disputed territory.

The hearing, announced by a lawyer for the movement on Thursday, should test Polisario’s use of a European court ruling last year that said Western Sahara should not be considered part of Morocco in European Union and Moroccan deals.

The Marshall Island-flagged NM Cherry Blossom, seized by maritime court order in Port Elizabeth on South Africa’s east coast since Monday, was carrying 50,000 tonnes of phosphate to New Zealand from Laayoune in the Moroccan-controlled part of the disputed territory for Morocco’s OCP phosphate export company.

Western Sahara has been disputed since war broke out in 1975 between Morocco and the Polisario movement fighting for the Sahrawi people’s independence there. A 1991 ceasefire split the region into separate parts controlled by Morocco and Polisario.

“On the 18 May we will be seeking a final order saying that the cargo will remain interdicted from leaving the jurisdiction of the court until such time as my client’s court case for the return of the property is heard,” said Andre Bowley, the Polisario movement’s lawyer, in Cape Town.

The temporary order means the NM Cherry Blossom remains at anchor in the Bay of Algoa under the jurisdiction of Port Elizabeth.

OCP has said it expects a quick resolution once the details of the case are heard. Morocco’s government said on Thursday it did not expect Polisario’s legal challenge would succeed.

“There have been failed attempts to undermine Morocco’s territorial integrity in the past and future attempts will fail again,” government spokesperson Mustapha El Khalfi told reporters in Rabat.

Bowley told Reuters the temporary court order makes provision for OCP and five other respondents, including the ship owners and the New Zealand buyers of the cargo, to put up financial security in lieu of the phosphate shipment.

“If you want to carry on sailing with the phosphate onboard the ship, then fine, put up a bank guarantee securing the amount and value of the phosphate, then the ship can depart,” he said, adding the estimated value of the cargo was around $5 million.

Morocco and Polisario have been locked in diplomatic and legal battles since 1991. U.N. peacekeepers had to step when tension flared in between Moroccan forces and Polisario brigades in the buffer zone near the Mauritania border.

In January, Morocco rejoined the African Union regional body, where Polisario’s self-declared Sahrawi Arab Democratic Republic (SADR) is also a member. South Africa along with Algeria have been key supporters of the SADR. (Additional reporting by Samia Errazzouki in Rabat; Editing by Patrick Markey and Tom Heneghan)